Planar antennas are typically mounted on dielectric substrates to facilitate their use in hybrid circuits. They have been used extensively on substrates having low dielectric constants.
As the demand for high frequency devices has increased, however, substrates with low dielectric constants have become less and less useful. The parasitic reactances of the hybrid circuits have a significant detrimental effect on the operability of the constituent devices at high frequency.
It has become desirable, therefore, to implement planar antennas on higher dielectric semiconductor substrates. Monolithic integrated circuits which include the devices, antennas and associated interconnects would greatly improve high frequency performance. Unfortunately, efficient planar antennas have been difficult to implement on uniform semiconductor substrates. Because of the high dielectric constant of semiconductors, most of the radiation emitted by the antenna passes into and is trapped by the substrate, resulting in inefficient antennas. In these conventional integrated circuits, the higher the dielectric constant of the substrate, the less efficient the planar antenna.
Several techniques have been proposed to solve this problem. One technique is to place a conducting plane on the bottom surface of the substrate opposite the antenna. The conductor reflects radiation back toward the top surface. However, the power radiated through the top surface is increased by only about a factor of two. Most of the power still remains trapped in the substrate.
A second approach is to modify the bottom surface so that all of the radiation escapes. This is accomplished with a hyper-hemispherical lensing element having the same dielectric constant as the substrate. The problem with this approach is that the lensing element is so large as to be incompatible with integrated circuits.